Wow. A lot of misinformation here. Car 318's had forged cranks in 1967 only. From 1968 up 273's and 318's had cast cranks. Not that it really matters since they are plenty strong. 340's had forged, shot peened cranks with drilled throws, see post#76, from 1968-1972 partial. 1972 partial and 1973 340's had cast cranks externally balanced. All 273's, 318's, and 1968-1972 partial 340's were internally balanced. All 273's and 340's had floating, brass bushed pin, rods. 318's had floating, light rods, and pressed pin, heavy rods. The heavy duty rod forgings could be found in 340's, 360's and later 318's and had the same forging # in the same time period.
As for the 318/340 internals, it makes little sense to discuss unless you know what internals we are talking about. What does it matter if the OP drives it and it performs to his satisfaction and does not vibrate, like it is out of balance, he should be good to go.